Just like your skin, your hair and nails are affected by the foods you choose to eat. And we're not talking about the sheen of those lustrous waves or a hangnail. Both hair and nails can become brittle and dry, and hair can thin or fall out without the right range of nutritious picks in your diet.
"Both are a barometer of how well (or how poorly) you're feeding the body," says dermatologist Jessica Wu, M.D., author of "Feed Your Face" and skin and beauty expert for Daily Glow, "as well as your overall health."
Both hair and nails are made from the same protein, called keratin, so it makes sense that similar diet choices would affect them both, she explains. Of course, a number of other lifestyle choices also play a role, including smoking, she says, since it reduces circulation and may cut down on the amount of biotin in the blood. Biotin, often added to hair and nail products, seems to strengthen both.
Less research exists to document the impact of various foods on hair and nail health than to illustrate the role of diet in healthy skin. But there are still a few foods to consider avoiding if you're concerned about brittle nails or thinning hair.
Wu says she spends a good amount of time discussing diet with patients who come to her with thinning hair or brittle nails. One of the main culprits in her Los Angeles office is too much fish. "Some fish contain high levels of mercury, and high levels of mercury can lead to hair loss," she says. These patients are eating a lot of fish, she stresses, and particularly sushi, sometimes four or five times a week. While true mercury poisoning is rare, swordfish and mackerel do have high levels of mercury, as do certain varieties of tuna. Canned light tuna, salmon and shrimp are all low in mercury, according to the FDA.
"Just like sugar is bad for the skin in many ways, foods that are sugary are bad for your hair and nails," says Wu. Eating sweets causes blood sugar to spike. As the body pumps out insulin in response to the rise in blood sugar, it also raises levels of androgen, a male hormone that can make the hair follicle shrink in both women and men, she says.
It follows, then, that foods that are quickly broken down into sugar pose similar hair and nail risks. Starchy white breads, pastas and cakes trigger a similar response in the body, says Wu, and can lead to hair thinning. Research has shown that a high-glycemic-index diet can increase androgen levels, while a low-glycemic-index diet can reduce them.
Too Much Vitamin A
In ultra-high doses, vitamin A can lead to hair loss. A typical multivitamin won't usually contain a dangerous amount, according to JoyBauer.com, but an individual vitamin A supplement might. It's also related to compounds found in some medications, says Wu, like Accutane, which could be why hair thinning is a side effect of some treatments, she says.
Since hair and nails are made of protein, people who don't get enough in their diet may experience brittle nails or hair loss, says Wu. Typically, this only occurs in people with severe diet limitations or eating disorders, she says.
Vegetarians should keep in mind that protein doesn't have to come from meat -- beans, tofu, spinach, lentils and more are all beneficial. Foods with a particular amino acid that creates keratin, called cystine, can also help, like pork, broccoli, wheat germ and red peppers, says Wu.
There's a misconception that little white flecks in your nails may indicate a calcium deposit. According to Reader's Digest, those spots might be a sign your diet is lacking in zinc. Both zinc and iron -- found together naturally in red meats and some seafood -- are essential to keratin formation, says Wu, so skimping on these can cause hair and nail problems. Getting enough can be challenging for vegetarians and vegans, she says. Luckily, both zinc and iron are found naturally in some beans.